Method of testing a communication system using a portable wideband antenna-radiated signal generator

ABSTRACT

A portable wideband harmonic signal generator includes circuitry for generating a signal having a selected fundamental frequency, for producing a signal having a harmonic series of the selected fundamental frequency, for transferring the signal having the harmonic series using a balanced impedance output, and for directionally transmitting transferred signal having the harmonic series using a directional antenna having a characteristic impedance that is matched to the balanced impedance output. There is thus provided a compact, efficient transmitter and antenna assembly for transmitting a wideband signal.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This application is a divisional of prior U.S. patent application Ser.No. 13/167,935 filed on 24 Jun. 2011 and claims the benefit under 35U.S.C. §121 of the prior application's filing date.

CROSS REFERENCE TO OTHER PATENT APPLICATIONS

This patent application is co-pending with the following related U.S.patent application Ser. No. 13/167,935 by the same inventors, Richard S.Frade and Kenneth White.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to high frequency communications and isdirected more particularly to a design for a portable widebandantenna-radiated signal generator.

(2) Description of the Prior Art

Often, personnel such as EM (electromagnetic) and communicationengineers/technicians require a test signal to be generated in order toperform continuity tests of an RF (radio frequency) transmission paththrough an antenna that is coupled to a receiver. To perform such tests,the personnel are often required to carry relatively expensive,sensitive, large, and heavy test equipment that inconveniently rely uponline power. The testing is especially even more problematic whenoperating on vessel platforms such as submarines where personnel arerequired to carry the test equipment through the submarine sail toconduct the test. Commonly encountered difficulties encountered whileperforming the tests include requirements that personnel must carryheavy and bulky test equipment, that expensive equipment be available,procedures that entail long test setup and breakdown times, and the needfor ship power to power the test equipment.

In the prior art, wideband signal generation is addressed:

In Telewski (U.S. Pat. No. 3,777,271), a step recovery diode is drivenby two or more frequencies to form a harmonic generator.

In McEwan (U.S. Pat. No. 5,274,271), an output pulse generator forwideband applications is disclosed.

In Nelson et al. (U.S. Pat. No. 5,369,373) the step recovery diode 14 isdisclosed that is driven by a sine-wave oscillator 12. In response, awideband series of harmonics of the fundamental frequency is produced byfrequency oscillator 12. The output of the step recovery diode 14 issupplied to one or more bandpass filters or lowpass filters whichprovide selection windows so that only a specified number of harmoniclines are passed within a selection window.

In Nellson, (U.S. Pat. No. 5,793,309) a short-range electromagnetictransceiver is disclosed in which an oscillator 14 excites a steprecovery diode 12. The output of step recovery diode 12 is provided to afilter 24 that acts as a harmonic filter and selects the particularfrequency of transmission. The output of filter 24 is gated to produce ashort RF pulse which is a harmonic of the input excitation signal and isin the GHz range. The short RF pulse is propagated normal to the circuitand through space until it is dissipated or reflected from a target backinto the antenna 20.

As indicated in the references above, a need still exists for anefficient portable wideband antenna-radiated signal generator systemdesign. An additional need exists for an energy efficient method forproducing a wideband antenna-radiated signal.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention is to provide acompact high efficiency transmitter and antenna.

It is a further object of the present invention to provide an energyefficient method for producing a non-gated continuous wave widebandantenna-radiated signal. Other objects and advantages of the presentinvention will be apparent from reading the disclosure herein.

In accordance with the present invention, a portable wideband harmonicsignal generator includes circuitry for generating a signal having aselected fundamental frequency, for producing a signal having a harmonicseries of the selected fundamental frequency, for transferring thesignal having the harmonic series using a balanced impedance output, andfor directionally transmitting transferred signal having the harmonicseries using a directional antenna having a characteristic impedancethat is matched to the balanced impedance output. There is thus provideda compact, efficient transmitter and antenna assembly for transmitting awideband signal.

The above and other features of the invention, including various noveldetails of construction and combinations of parts, will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claims. It will be understood that the particularassembly embodying the invention is shown by way of illustration onlyand not as a limitation of the invention. The principles and features ofthis invention may be employed in various and numerous embodimentswithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beapparent with reference to accompanying drawings in which is shown anillustrative embodiment of the invention, wherein correspondingreference characters indicate corresponding parts throughout the severalviews of the drawings and wherein:

FIG. 1 is a diagram of a system implementing one embodiment of thecurrent invention;

FIG. 2 is a diagram of a system implementing another embodiment of thecurrent invention;

FIG. 3 is a diagram of a impedance matching and drive network for a steprecovery diode of an embodiment of the current invention;

FIG. 4 is a diagram that illustrates an ideal frequency input andidealized frequency response of an embodiment of the network of FIG. 3in accordance with the current invention;

FIG. 5 is a diagram of a tapered micro-stripline of an embodiment of thecurrent invention;

FIG. 6 is a diagram that illustrates a frequency response of the anembodiment of the tapered micro-stripline of FIG. 5 in accordance withthe current invention; and

FIG. 7 is a diagram of a system implementing a further embodiment of thecurrent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, across-sectional, view of the proximal end and side of an exemplaryportable wideband antenna-radiated signal generator is shown andreferenced generally by numeral 10. Signal generator 10 includes ahousing 12 that is arranged to be easily held in a single hand of auser. Housing 12 encases (and/or otherwise captivates) power unit 14,human interface (not shown), wideband generator 18, balun 20, antenna22, and optional laser designator 26. Housing 12 thus provides a commonassembly for mounting various components of the signal generator

Power unit 14 includes a power source (such as a battery) and iscontrollably actuated in response to mechanical actions and/orelectrical commands generated human interface. For example, initialactuation of power unit 14 causes power to be supplied to widebandgenerator 18.

The human interface 16 is arranged to allow a user to select operatingparameters for controlling wideband generator 18. For example, a usercan select a fundamental frequency (from 0 Hz to over 1.5 GHz) forgenerating a wideband signal (based on the selected fundamentalfrequency), output power of the wideband generator, output signalharmonic spacing, and operating mode (such as “off,” “stand-by,” and“normal”).

The wideband generator includes (and as discussed further below withrespect to FIG. 2) a programmable signal generator for producing avariable fundamental frequency signal. The variable fundamentalfrequency signal is coupled (directly or indirectly) to a step-recoverydiode to produce an output signal that includes series of harmonics.

The output signal is coupled to balun 20 for wideband impendencematching. Balun 20, for example, is a tapered stripline having 50 ohms(unbalanced) input impedance and 20 ohms (balanced) output impedance. Atapered stripline exhibits the characteristic of passing frequencieshaving wavelengths greater than around twice the length of the taperedportion of the tapered stripline. An example balun is discussed belowwith reference to FIG. 5 and FIG. 6.

The output of balun 20 is coupled to antenna 22. Antenna 22 is arrangedto maximize the efficiency of radiation and directionality of a widebandradiated signal 24 (thus contributing to the overall efficiency ofsignal generator 10). In an embodiment, antenna 20 is a traveling waveantenna arranged as a “vee” (V-shaped) dipole antenna. Thus, antenna 20is a passive component that exhibits relatively flat impedancecharacteristics over a wide range of input frequencies and minimizesreflection of input frequencies. When the fundamental frequency beingbroadcast has a wavelength that is greater than five times the length“l” of the antenna 20, termination is not typically required. Otherwise,proper termination of antenna 20 results in substantially noreflections.

Each of the radiators of antenna 20 are arranged in a vee-shaped patternhaving an angle of 2θ (where the angle θ is the angle between oneradiator and the central axis of propagation of wideband radiated signal24). The radiators of antenna 20 arranged with the proximal portion ofthe antenna 20 having the radiators more closely spaced together and thedistal portion of the antenna 20 having ends of the radiators spacedfurther apart. Angle 2θ can be selected to maximize constructiveinterference of sidelobes radiated by each radiator along the centralaxis of propagation of wideband radiated signal 24.

The housing 12 of signal generator 10 includes an optional laser 26 fordesignating a point in an area (e.g., for targeting purposes) that isirradiated by the signal generator 10. Laser 26 is controlled by thehuman interface and powered by power unit 14. Laser 26 can be configuredto produce laser beam 28 in response to the signal generator 10 beingprogrammed to radiate power. Thus, laser 26 can also serve as a warningindicator that the signal generator is actively transmitting.

Referring now to FIG. 2, a diagram of another embodiment of portablewideband antenna-radiated signal generator is shown. Signal generator 30includes a battery 32 for purposes of supplying power to electricalcomponents of the signal generator 30. The battery 32 (as well as theother components of signal generator 30) is sized to fit with in ahand-held housing of the signal generator 30. The power output ofbattery 32 is coupled to power regulation circuit 34 for control andregulation.

Micro-controller 36 is arranged to provide and receive human commands toand from a human interface 38. For example, a user can use the humaninterface 38 to provide commands for controlling the signal generator,such as providing a command to activate (e.g., “turn on”) or deactivatethe signal generator 30.

Such commands are received by the micro-controller 36, which in turn(for example) sends control signals to the power regulation circuit 34for switchably coupling power from the battery 32. The micro-controller36 is arranged to control other components of the signal generator 30 asfurther described below. In various modes of operation themicro-controller 36 may offer differing test scenarios to a user (fromwhich the user can select a particular test scenario). Each testscenario includes a list of values of various operating parameters, sothat the user is not required to individually enter each of theoperating parameters of a particular test scenario.

The micro-controller 36 is arranged to control DDS (direct digitalsynthesizer) 40 to provide a selectable fundamental frequency, which isselected from a range including for example, from DC (direct current) toa frequency above 1.5 GHz. DDS 40 typically includes a crystaloscillator reference and is programmable in real time to produce aselected frequency. The frequency of the fundamental frequency isselected, for example, in response to a command received by the userinterface 38. The DDS 40 is controllably powered by power regulationcircuit 34.

RF amplifier 42 is coupled to the output of DDS 40 such that the RFamplifier 42 receives a fundamental frequency signal having a frequencyas programmed by the micro-controller 36. The RF amplifier is arrangedto receive a command from the micro-controller 36 to specify an amountby which to amplify the received fundamental frequency signal. The RFamplifier 42 is controllably powered by power regulation circuit 34.

RF switch 44 is coupled to the output of the RF amplifier 42 to receivethe amplified fundamental frequency signal. The RF switch 44 is arrangedto receive a command from the micro-controller 36 to specify whether theamplified fundamental frequency signal is to be coupled to a lowerfrequency bypass path or a harmonic generator frequency path (whichtends to act as a high-pass filter). The lower frequency bypass path istypically used when broadcast signals of the signal generator 30 havelower frequencies (e.g., from direct current to around 1.5 GHZ). Usingthe lower frequency bypass path when testing lower frequency responsescan be used to avoid high-pass filtering (by impedance matchingcomponents such as wideband matching network 64, discussed below) oflower frequency components of the signal to be broadcast by signalgenerator 30.

Accordingly, low-frequency matching network 46 is arranged to receivethe amplified fundamental frequency signal when the RF switch 44 isconfigured to couple the amplified fundamental frequency signal to thelow-frequency matching network 46. The low-frequency matching network 46is arranged to receive the amplified fundamental frequency signal in anunbalanced medium and to provide the amplified fundamental frequencysignal using a medium that is balanced with respect to transmittingwide-band antennas 54.

The harmonic generator frequency path is selected when the RF switch 44is arranged to couple the amplified fundamental frequency signal (e.g.,received from the RF amplifier 42) to the drive and bias network 48.When the harmonic generator frequency path is selected, the drive andbias network is arranged to stabilize, match impedances, and drive theSRD (step recovery diode) 50. The SRD 50 is a microwave diode havingsteep doping profiles and relatively narrow junctions for optimizingdiode charge storage. The fast recovery of injected charge for the SRD50 provides a rapid transition period and efficiently produces a widerange of harmonics of the frequency of the amplified fundamentalfrequency signal. The operation of drive and bias network 48 and SRD 50are described more fully below with respect to FIG. 3 and FIG. 4.

The wideband harmonic output of SRD 50 is coupled to wideband matchingnetwork 52. A wideband matching network 52 matches the impedance of theoutput of SRD 50 with the wideband antennas 54. An example of a widebandmatching network 52 is described below with respect to FIG. 5 and FIG.6. An example of wideband antennas 54 is antenna 22 that is describedabove with respect to FIG. 1.

Referring now to FIG. 3, the operation of drive and bias network 48 andSRD 50 is now described. A network 56 is formed by (passive) componentschoke 58, capacitor 60, and resistor 62, capacitor 64, choke 66,capacitor 68, and choke 70 coupled to SRD 50. The network 56 receives aninput signal that includes a fundamental frequency at node Vin andprovides an output signal at node Vout that includes harmonics of thereceived fundamental frequency of the input signal.

The amplified fundamental frequency signal (from the RF amplifier 42,for example) is received at input node Vin. Choke 58, capacitor 60, andresistor 62 are arranged as a high-pass filter for increasing thestability of the output of the SRD 50. Resistor 62 is selected to biasthe input voltage of the SRD 50. A low-pass filter is formed bycapacitor 64 and choke 66 and is arranged to match the impedance of thenetwork 56 with the source impedance of the incoming amplified frequencysignal. A second low-pass filter is formed by capacitor 68 and choke 70and is arranged to drive and enhance harmonic frequencies output by SRD50.

Referring now to FIG. 4, the input and output frequency characteristicsof network 56 are discussed. Plot 72 represents an idealized fundamentalfrequency (generated by DDS 40, for example) that is provided as aninput to network 56. Plot 74 represents an idealized frequency responseof network 58 to the input fundamental frequency. Plot 74 illustrates aseries of harmonics of the fundamental frequency wherein the amplitudeof each harmonic generally decreases with increasing distance (infrequency) of each harmonic from the input fundamental frequency. Thus,when the fundamental frequency is adjusted (by changing a controllableinput of DDS 40, for example), the spacing and location of theillustrated harmonics vary in response to the change of the fundamentalfrequency. The output of network 56 is typically coupled to a widebandmatching network, such as balun 20.

Referring now to FIG. 5, a wideband matching network for matching theoutput impedance of a harmonic generator to an input impedance of awideband antenna is discussed. Wideband matching network 56 isillustrated as a (passive) tapered micro-stripline 78. Taperedmicro-stripline 78 includes an input section 80, the tapered/middlesection 82, and an output section 84. Input (proximal) section 80 has acharacteristic impedance of around 25 ohms and is about 30 mils wide.Tapered/middle section 82 has a length 76 that extends about 300 milslengthwise and has a width that gradually tapers over the 300 mildistance of about 30 mils wide to about five mils wide. Output (distal)section 84 has a characteristic impedance of around 50 ohms and is aboutfive mils wide. Thus, the characteristic impedance of taperedmicro-stripline 78 gradually varies from input impedance of 25 ohms toan output impedance of 50 ohms across the length 76 of the middlesection 82. The frequency response of the tapered micro-stripline 78 isnow discussed with reference to FIG. 6.

FIG. 6 illustrates the frequency response of the tapered micro-striplineas illustrated in FIG. 5. Plot 86 generally illustrates a frequencyresponse of the tapered micro-stripline 78 over a range inputfrequencies extending from direct current (DC) to 50 GHz. For example, aresponse such as “return loss” in dB is illustrated using curve 88 and a“reflection coefficient” (as a linear function) is illustrated usingcurve 90. The response to frequencies higher than the illustrated 50 GHzare similar to the responses illustrated in the 10-50 GHz portion ofplot 86. In particular, the maximum amplitudes for input frequenciesgreater than around 10 GHz (theoretically) maintains a value of around−40 dB as the input frequencies extended towards infinity. Thus, thetapered micro-stripline is arranged to efficiently transmit higherfrequencies without appreciable “roll-off” (e.g., progressively higherattenuation of higher frequencies) of the higher-end harmonics producedby an SRD such as SRD 50.

FIG. 7 illustrates testing of a communication system using a portablewideband antenna-radiated signal generator. Vessel 92 includes arelatively inaccessible area such as a sail area 94, wherein the sailarea 94 includes components of a communication system that are to betested. The components include visible components (such as an antenna96) and hidden components (such as cabling and transceivers, not shown).A portable wideband antenna-radiated signal generator (such as signalgenerator 10) is used to externally irradiate antenna 96 for testing(for example) continuity from the antenna 96 to a transceiver within thevessel 92. The signal generator 10 is typically used at location that isproximate to the sail and is around 3 meters distance from a targetantenna. The signal generated by signal generator 10 can be measuredusing equipment coupled to components of the communication system withinvessel 92. Thus, the signal generator 10 can be used to easily andefficiently test components of a communication system, even whencomponents of the communication system are included in a relativelyinaccessible area. Likewise, the signal generator 10 can be used toeasily and efficiently test components of the communication system evenwhen relatively expensive assets (such as non-hand-portable testequipment and/or satellite communications) are not available orrelatively costly to use.

Additionally, the signal generator 10 can be used to performsignal-to-ratio (SNR) tests in conjunction with available communicationsystem assets. For example, a satellite 98 can establish a communicationsession with a transceiver aboard vessel 92 via antenna 96. A user can,for example, select a fundamental frequency or frequency spacing (suchas the “comb” spacing of harmonics) and power level for a signal to betransmitted from the signal generator 10. (As discussed above, a usercan select a test scenario, which then selects test parametersappropriate for programming operational parameters of the signalgenerator 10 to act as a signal generator for a particular testscenario.) The level of the power output of the signal generator 10, thedistance of the signal generator 10 to the antenna 96, the frequencyand/or frequency spacing of the output power of the signal generator 10,and the measured strength of a signal from the satellite 98 can be usedto determine the SNR response of the communication system.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed and illustrated in order to explain the nature of theinvention, may be made by those skilled in the art within the principleand scope of the invention as expressed in the appended claims.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description only. Itis not intended to be exhaustive nor to limit the invention to theprecise form disclosed; and obviously many modifications and variationsare possible in light of the above teaching. Such modifications andvariations that may be apparent to a person skilled in the art areintended to be included within the scope of this invention as defined bythe accompanying claims.

What is claimed is:
 1. A method of testing a communications system atleast partially included within a submarine sail comprising: aiming ahand-held wideband harmonic signal generator at a selected receivingantenna that is mounted on the submarine sail, wherein the aiming isperformed from a location that is proximate to the selected receivingantenna mounted on the submarine sail, wherein the hand-held widebandharmonic signal generator includes circuitry for generating a signalhaving a selected fundamental frequency, for producing a signal having aharmonic series of the selected fundamental frequency, for transferringthe signal having the harmonic series using a balanced impedance output,for directionally transmitting transferred signal having the harmonicseries using a directional antenna having a characteristic impedancethat is matched to the balanced impedance output; irradiating theselected receiving antenna to produce an induced signal using thedirectionally transmitted signal having the harmonic series generated bythe hand-held wideband harmonic signal generator; and measuring theinduced signal in the communications system of the submarine.
 2. Themethod in accordance with claim 1 wherein the harmonics of the selectedfundamental frequency are generated by a step recovery diode (SRD) andhave a frequency spacing that is selected by varying the selectedfundamental frequency.
 3. The method in accordance with claim 1 furthercomprising: receiving a signal from a satellite using the selectedreceiving antenna; and comparing the received satellite signal with theinduced signal.
 4. The method in accordance with claim 1 furthercomprising: illuminating the selected receiving antenna using a laserthat is affixed to the hand-held wideband signal generator.